The invention concerns an autofocus module for a microscope-based system having an objective that defines an optical axis in which an illuminating light beam, which is perpendicular to a surface of a specimen onto which focusing occurs, propagates.
The invention further concerns a microscope system having an objective that defines an optical axis which is perpendicular to the surface of a specimen, and having a stage on which the specimen rests and which is displaceable in the direction of the optical axis.
In addition, the invention concerns an autofocus method for a microscope-based system which encompasses at least one objective that defines an optical axis of the microscope-based system.
German patent document DE 32 19 503 describes an apparatus for automatic focusing on specimens to be viewed in optical devices. After reflection at the surface of a specimen and reflection at a splitter mirror, the reflected measured light beam passes through a pinhole. A portion of the measured light beam is reflected out by means of a fully reflective surface and, after passing through a slit diaphragm, is directed onto a differential diode. In the focused state, the focus is located between the two diodes. Upon defocusing, the measurement spot migrates onto one of the two diodes, which are connected to corresponding control means. Optical or mechanical means of the microscope are adjusted by the control means to as to bring the measurement spot once again between the two diodes and thus re-establish the focal position.
European Patent Application EP-A-0 124 241 describes a microscope having an automatic focusing device. The microscope encompasses a storage device for saving the data for the objectives that are used in the microscope. Also provided is a control device that monitors and regulates the various microscope functions. The tasks of the control device also include moving the focusing stage. A CCD element, which receives an image from the respectively selected objective and, together with a calculation unit, ascertains the image sharpness from the optimum contrast, is provided as an image acquisition device. The objective data of the objective currently being used must be taken into account in ascertaining the optimum degree of sharpness. These data are, as already mentioned above, stored in a memory.
German Unexamined Application DE 41 33 788 describes a method for autofocusing of microscopes and an autofocus system for microscopes. The image of a specimen or of a pattern superimposed onto the specimen is conveyed to two regions on a detector or to two different detectors, such that in the focused position, one image occurs in front of one detector, and one image behind the other detector. The image sharpness states on the detectors are converted into electronic signals whose difference is used to focus the objective. The distances of the image or of the respective pattern from the respective detectors are adjustable. Deliberate offset settings as well as “IR offset” correction settings can be implemented.
In the context of automatic focusing in microscopes in the semiconductor industry, it is problematic that transitions from highly reflective regions to less-reflective regions cause an autofocus system to make incorrect settings. These transitions are referred to as “edges.” The influence of these edges on focusing using an autofocus system is referred to in the description below as the “edge effect.”